1. Field of the Invention
The subject matter disclosed generally relates to a drive roller assembly for a mobile robot.
2. Background Information
There have been developed various mobile robots that have a variety of different drive mechanisms to power the robot across a surface. For example, U.S. Pat. No. 5,374,879 issued to Pin et al., discloses a holonomic platform that includes three separate drive roller assemblies. Each drive roller assembly includes a pair of rollers that are spun by a drive motor. The rollers periodically make contact with the ground to exert a frictional force that propels the robot across a surface.
One or more of the three rollers assemblies is typically powered to drive the robot in a desired direction. The rollers of each roller assembly are coupled to the motor by a bracket. The bracket allows passive movement of the rollers that are not driven by a motor. Unfortunately, the brackets prevent continuous contact between a single roller and the underlying surface of the robot. For this reason each roller assembly requires two rollers that operate out of phase so that one roller is always in contact with the surface.
application Ser. No. 206,457 filed in the name of Wang et al. and assigned to the assignee of this application, InTouch Health, Inc. discloses a holonomic platform for a remote controlled robot. The platform includes three separate roller assemblies. Each roller assembly includes a pair of transmission rollers that engage and spin a drive ball. Rotation of the drive ball moves the robot across a surface. Like the Pin device of the prior art the transmission rollers of each subassembly are coupled to a motor by a bracket. The bracket allows desirable passive movement of the transmission rollers but prevents continuous contact between a single roller and the drive wheel.
The rollers operate out of phase so that one of the rollers is always in contact with the drive ball. If the relative phase of the rollers changes, the movement of the robot may develop a wobble. Additionally, the out of phase rotation of the transmission rollers may create undesirable impact forces and resultant stresses on the drive ball and supporting bearings. The impact forces require usage of a relatively hard drive ball.